.TH std::atomic_flag_wait,std::atomic_flag_wait_explicit 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::atomic_flag_wait,std::atomic_flag_wait_explicit \- std::atomic_flag_wait,std::atomic_flag_wait_explicit

.SH Synopsis
   Defined in header <atomic>
   void atomic_flag_wait( const atomic_flag* object, bool old )       \fB(1)\fP \fI(since C++20)\fP
   noexcept;
   void atomic_flag_wait( const volatile atomic_flag* object,         \fB(2)\fP \fI(since C++20)\fP
                          bool old ) noexcept;
   void atomic_flag_wait_explicit( const atomic_flag* object,
                                   bool old, std::memory_order order  \fB(3)\fP \fI(since C++20)\fP
   ) noexcept;
   void atomic_flag_wait_explicit( const volatile atomic_flag*
   object,                                                            \fB(4)\fP \fI(since C++20)\fP
                                   bool old, std::memory_order order
   ) noexcept;

   Performs atomic waiting operations.

   Compares object->test(std::memory_order_seq_cst) or object->test(order) with old,
   and if they are equal then blocks until *object is notified by
   std::atomic_flag::notify_one() or std::atomic_flag::notify_all() (or the thread is
   unblocked spuriously). This is repeated until the values compare unequal.

   1,2) The memory synchronization order is std::memory_order_seq_cst.
   3,4) The memory synchronization order is order.
   If order is one of std::memory_order_release and std::memory_order_acq_rel, the
   behavior is undefined.

   These functions are guaranteed to return only if value has changed, even if
   underlying implementation unblocks spuriously.

.SH Parameters

   object - pointer to the atomic flag to check and wait on
   old    - the value to check the atomic flag no longer contains
   order  - the memory synchronization ordering

.SH Return value

   \fI(none)\fP

.SH Notes

   This form of change-detection is often more efficient than simple polling or pure
   spinlocks.

   Due to the ABA problem, transient changes from old to another value and back to old
   might be missed, and not unblock.

.SH Example

    This section is incomplete
    Reason: no example

.SH See also

   notify_one             notifies at least one thread waiting on the atomic object
   (C++20)                \fI(public member function of std::atomic_flag)\fP
   notify_all             notifies all threads blocked waiting on the atomic object
   (C++20)                \fI(public member function of std::atomic_flag)\fP
   atomic_flag_notify_one notifies a thread blocked in atomic_flag_wait
   (C++20)                \fI(function)\fP
   atomic_flag_notify_all notifies all threads blocked in atomic_flag_wait
   (C++20)                \fI(function)\fP

.SH Category:
     * Todo no example
